1. Field of the Invention
The present invention relates to a heat-treating method and apparatus used in the manufacture of a semiconductor device, an LC (liquid crystal) drive circuit board etc., and more in particular to an improved heat-treating method and apparatus for obtaining a better heat uniformity on an object to be treated.
2. Description of the Related Art
Various types of heat-treating apparatuses are employed in the manufacture of a semiconductor device, an LC (liquid crystal) drive circuit board and so on. In recent times, a sheet-by-sheet type heat-treating apparatus has been highlighted which heat-treats substrates, such as semiconductor wafers, in a sheet-by-sheet fashion. One of such heat-treating apparatuses is of an infrared lamp (halogen lamp) type and, in the manufacturing process of, for example, a semiconductor device, the same type of heat-treating apparatus is employed in the activation of an ion-implanted layer of the wafer by an anneal step.
In the heat treatment by the infrared lamp, the task is to obtain the uniform heating of an object to be treated. In the step of annealing a semiconductor wafer, a greater heat dissipation occurs at the marginal edge portion of the wafer, resulting in a lowering of a prevailing temperature. As a result, thermal nonuniformity is produced on the wafer surface and hence a slip line is produced at the marginal edge portion of the wafer to a greater extent. In order to overcome the problem, Japanese Patent Disclosure (Kokai) No. 62-128525 proposes the use of a ring-like temperature security member. In the technique of this Disclosure, a semiconductor wafer is placed on a silicon wafer support board and a guard ring (temperature security member) which is the same material as the semiconductor wafer is disposed around the semiconductor wafer. Under this condition, the wafer is illuminated with infrared lamps to carry out an anneal step. This method prevents a heat dissipation from the marginal edge portion of a to-be-treated wafer by the guard ring. The guard ring is made of the same material as that of the to-be-treated wafer.
The aforementioned technique surely prevents a heat dissipation from the marginal edge portion of the wafer and leads to a uniform heating on the surface of the wafer. On the other hand, that surface of the wafer which is located on the "support board" side is not heated by the infrared lamps due to the whole undersurface of the wafer being in face contact with the support board, thus causing thermal nonuniformity in a direction of the cross-section of the wafer and the occurrence of slip lines.
Furthermore, the face contact of the whole undersurface of the wafer with the support board degrades a load/unload operation with respect to the wafer and is liable to produce dust upon the loading and unloading of the wafer onto and out of the support board. This cannot meet a high-speed operation and a cleaning requirement demanded in a semiconductor device fabricating process.
The aforementioned problem is not restricted to an infrared lamp illumination type heat treating apparatus and arises as a common problem among various devices for the heat treatment of the substrate, such as a semiconductor wafer.